Impact of single and dual neoadjuvant HER2-directed therapy on clinical outcomes among patients with HER2-positive breast cancer (BC).
647 Background: While the addition of trastuzumab to neoadjuvant chemotherapy (CTX) is well established for HER2+ BC, the use of dual agent HER2 blockade in the preoperative setting is not considered standard of care. We conducted a comprehensive systematic review and meta-analysis to evaluate the impact of neoadjuvant dual and single agent HER2 blockade on breast conserving surgery (BCS), pathological complete response (pCR) for estrogen receptor (ER)+ and ER- tumors, and impact of pCR on disease-free survival (DFS) and overall survival (OS) for HER2+ BC. Methods: Based on QUORUM guidelines, MEDLINE and Cochrane Controlled Clinical Trials Register databases were queried to identify eligible trials. Inclusion criteria were prospective, neoadjuvant trials that had at least one arm with HER2 directed therapy, and reported pCR. Pooled relative risk ratios (RRs) and 95% confidence intervals (CIs) were estimated for endpoints using the random effects model. Results: We identified 34 trials (N = 4064). High pCR rates (> 40%) were seen with anthracycline-based CTX and trastuzumab, as well as taxane based CTX alone with dual HER2 blockade. The addition of trastuzumab to CTX did not improve BCS rate (RR 1.40, CI: 0.89-2.22, p=.15), but significantly increased rates of pCR (RR 1.91, CI: 1.38-2.64, p=.0001). Similarly, dual HER2 blockade compared to trastuzumab alone did not improve BCS rate (RR 1.03, CI: 0.77-1.38, p=.84), but significantly increased rates of pCR overall (RR 1.38, CI: 1.24-1.53, p<0.00001), in both ER+ (RR 1.72, CI: 1.14-2.61, p=.01) and ER- subsets (RR 1.91, CI: 1.38-2.64, p=.0001). Higher pCR was associated with improved DFS (RR 2.29, CI: 1.27-4.12, p=.006) and OS (RR 4.61, CI: 1.46-14.56, p=.009). Conclusions: Neither the addition of trastuzumab to CTX, nor the dual-HER2 blockade compared to trastuzumab, improves rates of BCS, but both significantly improve rates of pCR, which is associated with improved DFS and OS. A subgroup of HER2+ BC patients can achieve pCR with dual HER2 blockade without dependence on anthracycline-based therapy. Predictive biomarkers are needed to improve patient selection and personalize the optimal regimen for HER2+ BC.